1. Field of the Invention
Embodiments of the present invention generally relate to completion operations in a wellbore. More particularly, the present invention relates to a packer for sealing an annular area between two tubular members within a wellbore. More particularly still, the present invention relates to a packer having a bi-directionally boosted and held packing element.
2. Description of the Related Art
During the wellbore completion process, a packer is run into the wellbore to seal off an annular area. Known packers employ a mechanical or hydraulic force in order to expand a packing element outwardly from the body of the packer into the annular region defined between the packer and the surrounding casing. In addition, a cone is driven behind a tapered slip to force the slip into the surrounding casing wall and to prevent packer movement. Numerous arrangements have been derived in order to accomplish these results.
A disadvantage with known packer systems is the potential for becoming unseated. In this regard, wellbore pressures existing within the annular region between an inner tubular and an outer casing string act against the setting mechanisms, creating the potential for at least partial unseating of the packing element. Generally, the slip used to prevent packer movement also traps into the packing element the force used to expand the packing element. The trapped force provides the packing element with an internal pressure. During well operations, a differential pressure applied across the packing element may fluctuate due to changes in formation pressure or operation pressures in the wellbore. When the differential pressure approaches or exceeds the initial internal pressure of the packing element, the packing element is compressed further by the differential pressure, thereby causing it to extrude into smaller voids and gaps or exceed the compression strength of the packing element, thereby resulting in a compression set of the packing element. Thereafter, when the pressure is decreased, the packing element begins to relax. However, the internal pressure of the packing element is now below the initial level because of the volume transfer and/or compression set of packing element during extrusion. The reduction in internal pressure decreases the packing element's ability to maintain a seal with the wellbore when a subsequent differential pressure is applied or when the direction of pressure is changed, i.e. top to bottom.
Therefore, there is a need for a packer system in which the packing element does not disengage from the surrounding casing under exposure to formation pressure. In addition, a packer system is needed in which the presence of formation pressure serves to further compress the packing element into the annular region, thereby assuring that formation pressure will not unseat the seating element. Further still, a packer system is needed to maintain the internal pressure at a higher level than the differential pressures across the packing element. Further still, a packer system is needed to boost the internal pressure of the packing element above the differential pressure across the packing element. Further still, a packer system is needed that can boost the internal pressure of the packing element with equal effectiveness from differential pressure above or below the packing element.